30 Mr. R. Etheridge, Jun., on some Silurian Opercular 



like character, so far as my examination of these specimens 

 has gone. The rings are concentric and ridge-like, each sepa- 

 rate from the other, with well-marked interspaces between 

 them, the interspaces being quite double the width of the 

 ridges, if not a little more (PI. II. fig. 18). 



Three of the British-Museum specimens with the operculum 

 in place have the latter presented with the spiral whirls out- 

 wards ; and this surface is decidedly (although not very) con- 

 cave (PI. II. figs. 10 & 11). 



This is shown in a somewhat exaggerated form in the free 

 example, but heightened by fracture and compression from 

 above. On the other hand, in a fourth example, also with the 

 spiral side of the operculum exposed in place, the latter is 

 quite depressed conical (PI. II. fig. 12). 



Lastly, in a fifth specimen the circular form of the oper- 

 culum is well exhibited, and a somewhat different appearance 

 visible (PI. II. fig. 14). The operculum is depressed a little 

 immediately within the margin, and then rises at the centre 

 into a low spiral prominence. The surface is shining and 

 smooth, except near the margin, where there are a few very 

 fine spiral thread-like lines. This aspect is rather difficult of 

 explanation ; but I believe it to represent either the interior 

 of the plate or a cast of the interior, and to be reversed in 

 position. 



The five specimens here noticed are what is usually called 

 Euomphalus sculptus, J. de C. Sow.^, which was briefly de- 

 scribed as having the " surface ornamented with concentric 

 furrows and elevated lines." This description must have 

 been taken from a very much worn example ; for even in 

 indifferent specimens the close, transverse, undulating frills 

 of growth which cross these " elevated lines " are quite 

 visible. 



The characters of a well-preserved example of E. sculptus 

 are quite those assigned to another species, E. funatus, J. de 

 C Sow-tj viz., " Conical, very short ; ornamented with many 

 spiral threads, united by more numerous transverse lines ; 

 umbilicus rather small." 



It will be noticed that no mention is made of the number 

 of concentric ridges, or any approach thereto, in the respec- 

 tive species. On comparing the figures, however, it will be 

 seen that those on the body- whorl of E. funatus are much wider 

 apart and less numerous than those on a corresponding portion 

 of the shell of E. sculptus. 



* Murcliison's 'Silurian System,' p. 626, t. 12. f. 17. 

 t Min. Conch. 1824, v. p. 71, t. 450. f . 1 & 2 ; ' Silurian System,' p. 626, 

 t. 12. f. 20. 



